<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
    content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible"
    content="ie=edge">
  <title>Document</title>
</head>
<script>
  class SingleDog{
    show(){
      console.log('show');
    }
    static  getInstance(){
      if(!SingleDog.instance){
        SingleDog.instance=new SingleDog()
      }
      return SingleDog.instance
    }
  }
  const s1 = new SingleDog()
  const s2 = new SingleDog()
  console.log(s1===s2);
</script>
</html>
